This invention relates to the ion exchange of zeolites and provides a process for preparing ammonium zeolites of extremely low alkali metal content. In particular, the process involves ion exchange of a zeolite usually containing a significant amount of sodium to a potassium enriched form of the zeolite. Contact with an ammonium salt solution then provides the ammonium form zeolite with low alkali metal content.
Most zeolites (crystalline aluminosilicates) contain significant amounts of alkali metals, usually sodium. Many applications of said zeolites require the removal of nearly all the sodium and its replacement with ammonium ions. Many zeolite modifications such as stabilization also require removal of nearly all the sodium. Some zeolites including the faujasites have structures that impede the exchange of ammonium ion for sodium, especially when more than 70 to 80% of the sodium they contain is to be exchanged. Prior art methods include exhaustive ion exchange processes with solutions of high concentrations of ammonium salts. See Example IX of U.S. Pat. No. 3,449,020. An alternative process involves the steam calcination of an ammonium zeolite Y that still contains 2.5 to 5% Na.sub.2 O followed by an additional exchange with an ammonium salt solution. See U.S. Pat. No. 3,929,672 among others. This process is not always desirable, as some of the properties of the zeolite are changed and the hydrogen form of the zeolite is formed upon steam calcination. Not all zeolites of the faujasite structure are stable in the hydrogen form. U.S. Pat. No. 4,058,484 discloses a method for providing an ammonium zeolite which involves ion exchange with at least 20 equivalents of ammonium ions for each equivalent of sodium in the zeolite. The temperatures required for the exchange are very high, being in excess of 300.degree. F.
It is an object of this invention to provide ammonium zeolite X or ammonium zeolite Y by a method that does not involve temperatures above boiling, the use of ammonium salt solutions of high concentrations, and/or high ammonium ion to zeolite contact ratios.